Global hosting system

ABSTRACT

A network architecture or framework supports hosting and content distribution on a truly global scale. The inventive framework allows a Content Provider to replicate and serve its most popular content at an unlimited number of points throughout the world. The inventive framework comprises a set of servers operating in a distributed manner. The actual content to be served is preferably supported on a set of hosting servers (sometimes referred to as ghost servers). This content comprises HTML page objects that, conventionally, are served from a Content Provider site. A base HTML document portion of a Web page is served from the Content Provider&#39;s site while one or more embedded objects for the page are served from the hosting servers, preferably, those hosting servers near the client machine. By serving the base HTML document from the Content Provider&#39;s site, the Content Provider maintains control over the content.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Serial No. 12/753,988, filed Apr.5, 2010, now U.S. Pat. No. 8,073,961, which application was acontinuation of Serial No. 11/515,171, filed Sep. 1, 2006, now U.S. Pat.No. 7,693,959, which application was a continuation of Serial No.10/417,607, filed Apr. 17, 2003, now U.S. Pat. No. 7,103,645, whichapplication was a continuation of Serial No. 09/604,878, filed Jun. 28,2000, now U.S. Pat. No. 6,553,413, which application was a continuationof Serial No. 09/314,863, filed May 19, 1999, now U.S. Pat. No.6,108,703, which application was based on and claimed priority to SerialNo. 60/092,710, filed Jul. 14, 1998.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to information retrieval in a computernetwork. More particularly, the invention relates to a novel method ofhosting and distributing content on the Internet that addresses theproblems of Internet Service Providers (ISPs) and Internet ContentProviders.

2. Description of the Related Art

The World Wide Web is the Internet's multimedia information retrievalsystem. In the Web environment, client machines effect transactions toWeb servers using the Hypertext Transfer Protocol (HTTP), which is aknown application protocol providing users access to files (e.g., text,graphics, images, sound, video, etc.) using a standard page descriptionlanguage known as Hypertext Markup Language (HTML). HTML provides basicdocument formatting and allows the developer to specify “links” to otherservers and files. In the Internet paradigm, a network path to a serveris identified by a so-called Uniform Resource Locator (URL) having aspecial syntax for defining a network connection. Use of anHTML-compatible browser (e.g., Netscape Navigator or Microsoft InternetExplorer) at a client machine involves specification of a link via theURL. In response, the client makes a request to the server identified inthe link and, in return, receives a document or other object formattedaccording to HTML. A collection of documents supported on a Web serveris sometimes referred to as a Web site.

It is well known in the prior art for a Web site to mirror its contentat another server. Indeed, at present, the only method for a ContentProvider to place its content closer to its readers is to build copiesof its Web site on machines that are located at Web hosting farms indifferent locations domestically and internationally. These copies ofWeb sites are known as minor sites. Unfortunately, minor sites placeunnecessary economic and operational burdens on Content Providers, andthey do not offer economies of scale. Economically, the overall cost toa Content Provider with one primary site and one mirror site is morethan twice the cost of a single primary site. This additional cost isthe result of two factors: (1) the Content Provider must contract with aseparate hosting facility for each mirror site, and (2) the ContentProvider must incur additional overhead expenses associated with keepingthe minor sites synchronized.

In an effort to address problems associated with mirroring, companiessuch as Cisco, Resonate, Bright Tiger, F5 Labs and Alteon, aredeveloping software and hardware that will help keep minor sitessynchronized and load balanced. Although these mechanisms are helpful tothe Content Provider, they fail to address the underlying problem ofscalability. Even if a Content Provider is willing to incur the costsassociated with mirroring, the technology itself will not scale beyond afew (i.e., less than 10) Web sites.

In addition to these economic and scalability issues, minoring alsoentails operational difficulties. A Content Provider that uses a minorsite must not only lease and manage physical space in distant locations,but it must also buy and maintain the software or hardware thatsynchronizes and load balances the sites. Current solutions requireContent Providers to supply personnel, technology and other itemsnecessary to maintain multiple Web sites. In summary, mirroring requiresContent Providers to waste economic and other resources on functionsthat are not relevant to their core business of creating content.

Moreover, Content Providers also desire to retain control of theircontent. Today, some ISPs are installing caching hardware thatinterrupts the link between the Content Provider and the end-user. Theeffect of such caching can produce devastating results to the ContentProvider, including (1) preventing the Content Provider from obtainingaccurate hit counts on its Web pages (thereby decreasing revenue fromadvertisers), (2) preventing the Content Provider from tailoring contentand advertising to specific audiences (which severely limits theeffectiveness of the Content Provider's Web page), and (3) providingoutdated information to its customers (which can lead to a frustratedand angry end user).

There remains a significant need in the art to provide a decentralizedhosting solution that enables users to obtain Internet content on a moreefficient basis (i.e., without burdening network resourcesunnecessarily) and that likewise enables the Content Provider tomaintain control over its content.

The present invention solves these and other problems associated withthe prior art.

BRIEF SUMMARY

It is a general object of the present invention to provide a computernetwork comprising a large number of widely deployed Internet serversthat form an organic, massively fault-tolerant infrastructure designedto serve Web content efficiently, effectively, and reliably to endusers.

Another more general object of the present invention is to provide afundamentally new and better method to distribute Web-based content. Theinventive architecture provides a method for intelligently routing andreplicating content over a large network of distributed servers,preferably with no centralized control.

Another object of the present invention is to provide a networkarchitecture that moves content close to the user. The inventivearchitecture allows Web sites to develop large audiences withoutworrying about building a massive infrastructure to handle theassociated traffic.

Still another object of the present invention is to provide afault-tolerant network for distributing Web content. The networkarchitecture is used to speed-up the delivery of richer Web pages, andit allows Content Providers with large audiences to serve them reliablyand economically, preferably from servers located close to end users.

A further feature of the present invention is the ability to distributeand manage content over a large network without disrupting the ContentProvider's direct relationship with the end user.

Yet another feature of the present invention is to provide a distributedscalable infrastructure for the Internet that shifts the burden of Webcontent distribution from the Content Provider to a network ofpreferably hundreds of hosting servers deployed, for example, on aglobal basis.

In general, the present invention is a network architecture thatsupports hosting on a truly global scale. The inventive framework allowsa Content Provider to replicate its most popular content at an unlimitednumber of points throughout the world. As an additional feature, theactual content that is replicated at any one geographic location isspecifically tailored to viewers in that location. Moreover, content isautomatically sent to the location where it is requested, without anyeffort or overhead on the part of a Content Provider.

It is thus a more general object of this invention to provide a globalhosting framework to enable Content Providers to retain control of theircontent.

The hosting framework of the present invention comprises a set ofservers operating in a distributed manner. The actual content to beserved is preferably supported on a set of hosting servers (sometimesreferred to as ghost servers). This content comprises HTML page objectsthat, conventionally, are served from a Content Provider site. Inaccordance with the invention, however, a base HTML document portion ofa Web page is served from the Content Provider's site while one or moreembedded objects for the page are served from the hosting servers,preferably, those hosting servers nearest the client machine. By servingthe base HTML document from the Content Provider's site, the ContentProvider maintains control over the content.

The determination of which hosting server to use to serve a givenembedded object is effected by other resources in the hosting framework.In particular, the framework includes a second set of servers (or serverresources) that are configured to provide top level Domain Name Service(DNS). In addition, the framework also includes a third set of servers(or server resources) that are configured to provide low level DNSfunctionality. When a client machine issues an HTTP request to the Website for a given Web page, the base HMTL document is served from the Website as previously noted. Embedded objects for the page preferably areserved from particular hosting servers identified by the top- andlow-level DNS servers. To locate the appropriate hosting servers to use,the top-level DNS server determines the user's location in the networkto identify a given low-level DNS server to respond to the request forthe embedded object. The top-level DNS server then redirects the requestto the identified low-level DNS server that, in turn, resolves therequest into an IP address for the given hosting server that serves theobject back to the client.

More generally, it is possible (and, in some cases, desirable) to have ahierarchy of DNS servers that consisting of several levels. The lowerone moves in the hierarchy, the closer one gets to the best region.

A further aspect of the invention is a means by which content can bedistributed and replicated through a collection of servers so that theuse of memory is optimized subject to the constraints that there are asufficient number of copies of any object to satisfy the demand, thecopies of objects are spread so that no server becomes overloaded,copies tend to be located on the same servers as time moves forward, andcopies are located in regions close to the clients that are requestingthem. Thus, servers operating within the framework do not keep copies ofall of the content database. Rather, given servers keep copies of aminimal amount of data so that the entire system provides the requiredlevel of service. This aspect of the invention allows the hosting schemeto be far more efficient than schemes that cache everything everywhere,or that cache objects only in pre-specified locations.

The global hosting framework is fault tolerant at each level ofoperation. In particular, the top level DNS server returns a list oflow-level DNS servers that may be used by the client to service therequest for the embedded object Likewise, each hosting server preferablyincludes a buddy server that is used to assume the hostingresponsibilities of its associated hosting server in the event of afailure condition.

According to the present invention, load balancing across the set ofhosting servers is achieved in part through a novel technique fordistributing the embedded object requests. In particular, each embeddedobject URL is preferably modified by prepending a virtual serverhostname into the URL. More generally, the virtual server hostname isinserted into the URL. Preferably, the virtual server hostname includesa value (sometimes referred to as a serial number) generated by applyinga given hash function to the URL or by encoding given information aboutthe object into the value. This function serves to randomly distributethe embedded objects over a given set of virtual server hostnames. Inaddition, a given fingerprint value for the embedded object is generatedby applying a given hash function to the embedded object itself. Thisgiven value serves as a fingerprint that identifies whether the embeddedobject has been modified. Preferably, the functions used to generate thevalues (i.e., for the virtual server hostname and the fingerprint) areapplied to a given Web page in an off-line process. Thus, when an HTTPrequest for the page is received, the base HTML document is served bythe Web site and some portion of the page's embedded objects are servedfrom the hosting servers near (although not necessarily the closest) tothe client machine that initiated the request.

The foregoing has outlined some of the more pertinent objects andfeatures of the present invention. These objects should be construed tobe merely illustrative of some of the more prominent features andapplications of the invention. Many other beneficial results can beattained by applying the disclosed invention in a different manner ormodifying the invention as will be described. Accordingly, other objectsand a fuller understanding of the invention may be had by referring tothe following Detailed Description of the Preferred Embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference should be made to the following DetailedDescription taken in connection with the accompanying drawings in which:

FIG. 1 is a representative system in which the present invention isimplemented;

FIG. 2 is a simplified representation of a markup language documentillustrating the base document and a set of embedded objects;

FIG. 3 is a high level diagram of a global hosting system according tothe present invention;

FIG. 4 is a simplified flowchart illustrating a method of processing aWeb page to modified embedded object URLs that is used in the presentinvention;

FIG. 5 is a simplified state diagram illustrating how the presentinvention responds to a HTTP request for a Web page.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A known Internet client-server system is implemented as illustrated inFIG. 1. A client machine 10 is connected to a Web server 12 via anetwork 14. For illustrative purposes, network 14 is the Internet, anintranet, an extranet or any other known network. Web server 12 is oneof a plurality of servers which are accessible by clients, one of whichis illustrated by machine 10. A representative client machine includes abrowser 16, which is a known software tool used to access the servers ofthe network. The Web server supports files (collectively referred to asa “Web” site) in the form of hypertext documents and objects. In theInternet paradigm, a network path to a server is identified by aso-called Uniform Resource Locator (URL).

A representative Web server 12 is a computer comprising a processor 18,an operating system 20, and a Web server program 22, such as NetscapeEnterprise Server. The server 12 also includes a display supporting agraphical user interface (GUI) for management and administration, and anApplication Programming Interface (API) that provides extensions toenable application developers to extend and/or customize the corefunctionality thereof through software programs including Common GatewayInterface (CGI) programs, plug-ins, servlets, active server pages,server side include (SSI) functions or the like.

A representative Web client is a personal computer that is x86-,PowerPC- or RISC-based, that includes an operating system such as IBMOS/2 or Microsoft Windows '95, and that includes a Web browser, such asNetscape Navigator 4.0 (or higher), having a Java Virtual Machine (JVM)and support for application plug-ins or helper applications. A clientmay also be a notebook computer, a handheld computing device (e.g., aPDA), an Internet appliance, or any other such device connectable to thecomputer network.

As seen in FIG. 2, a typical Web page comprises a markup language (e.g.HTML) master or base document 28, and many embedded objects (e.g.,images, audio, video, or the like) 30. Thus, in a typical page, twentyor more embedded images or objects are quite common. Each of theseimages is an independent object in the Web, retrieved (or validated forchange) separately. The common behavior of a Web client, therefore, isto fetch the base HTML document, and then immediately fetch the embeddedobjects, which are typically (but not always) located on the sameserver. According to the present invention, preferably the markuplanguage base document 28 is served from the Web server (i.e., theContent Provider site) whereas a given number (or perhaps all) of theembedded objects are served from other servers. As will be seen,preferably a given embedded object is served from a server (other thanthe Web server itself) that is close to the client machine, that is notoverloaded, and that is most likely to already have a current version ofthe required file.

Referring now to FIG. 3, this operation is achieved by the hostingsystem of the present invention. As will be seen, the hosting system 35comprises a set of widely-deployed servers (or server resources) thatform a large, fault-tolerant infrastructure designed to serve Webcontent efficiently, effectively, and reliably to end users. The serversmay be deployed globally, or across any desired geographic regions. Aswill be seen, the hosting system provides a distributed architecture forintelligently routing and replicating such content. To this end, theglobal hosting system 35 comprises three (3) basic types of servers (orserver resources): hosting servers (sometimes called ghosts) 36,top-level DNS servers 38, and low-level DNS servers 40. Although notillustrated, there may be additional levels in the DNS hierarchy.Alternatively, there may be a single DNS level that combines thefunctionality of the top level and low-level servers. In thisillustrative embodiment, the inventive framework 35 is deployed by anInternet Service Provider (ISP), although this is not a limitation ofthe present invention. The ISP or ISPs that deploy the inventive globalhosting framework 35 preferably have a large number of machines that runboth the ghost server component 36 and the low-level DNS component 40 ontheir networks. These machines are distributed throughout the network;preferably, they are concentrated around network exchange points 42 andnetwork access points 44, although this is not a requirement. Inaddition, the ISP preferably has a small number of machines running thetop-level DNS 38 that may also be distributed throughout the network.

Although not meant to be limiting, preferably a given server used in theframework 35 includes a processor, an operating system (e.g., Linux,UNIX, Windows NT, or the like), a Web server application, and a set ofapplication routines used by the invention. These routines areconveniently implemented in software as a set of instructions executedby the processor to perform various process or method steps as will bedescribed in more detail below. The servers are preferably located atthe edges of the network (e.g., in points of presence, or POPs).

Several factors may determine where the hosting servers are placed inthe network. Thus, for example, the server locations are preferablydetermined by a demand driven network map that allows the provider(e.g., the ISP) to monitor traffic requests. By studying trafficpatterns, the ISP may optimize the server locations for the giventraffic profiles.

According to the present invention, a given Web page (comprising a baseHTML document and a set of embedded objects) is served in a distributedmanner. Thus, preferably, the base HTML document is served from theContent Provider that normally hosts the page. The embedded objects, orsome subset thereof, are preferentially served from the hosting servers36 and, specifically, given hosting servers 36 that are near the clientmachine that in the first instance initiated the request for the Webpage. In addition, preferably loads across the hosting servers arebalanced to ensure that a given embedded object may be efficientlyserved from a given hosting server near the client when such clientrequires that object to complete the page.

To serve the page contents in this manner, the URL associated with anembedded object is modified. As is well-known, each embedded object thatmay be served in a page has its own URL. Typically, the URL has ahostname identifying the Content Provider's site from where the objectis conventionally served, i.e., without reference to the presentinvention. According to the invention, the embedded object URL is firstmodified, preferably in an off-line process, to condition the URL to beserved by the global hosting servers. A flowchart illustrating thepreferred method for modifying the object URL is illustrated in FIG. 4.

The routine begins at step 50 by determining whether all of the embeddedobjects in a given page have been processed. If so, the routine ends. Ifnot, however, the routine gets the next embedded object at step 52. Atstep 54, a virtual server hostname is prepended into the URL for thegiven embedded object. The virtual server hostname includes a value(e.g., a number) that is generated, for example, by applying a givenhash function to the URL. As is well-known, a hash function takesarbitrary length bit strings as inputs and produces fixed length bitstrings (hash values) as outputs. Such functions satisfy two conditions:(1) it is infeasible to find two different inputs that produce the samehash value, and (2) given an input and its hash value, it is infeasibleto find a different input with the same hash value. In step 54, the URLfor the embedded object is hashed into a value xx,xxx that is thenincluded in the virtual server hostname. This step randomly distributesthe object to a given virtual server hostname.

The present invention is not limited to generating the virtual serverhostname by applying a hash function as described above. As analternative and preferred embodiment, a virtual server hostname isgenerated as follows. Consider the representative hostnamea1234.g.akamaitech.net. The 1234 value, sometimes referred to as aserial number, preferably includes information about the object such asits size (big or small), its anticipated popularity, the date on whichthe object was created, the identity of the Web site, the type of object(e.g., movie or static picture), and perhaps some random bits generatedby a given random function. Of course, it is not required that any givenserial number encode all of such information or even a significantnumber of such components. Indeed, in the simplest case, the serialnumber may be a simple integer. In any event, the information is encodedinto a serial number in any convenient manner. Thus, for example, afirst bit is used to denote size, a second bit is used to denotepopularity, a set of additional bits is used to denote the date, and soforth. As noted above in the hashing example, the serial number is alsoused for load balancing and for directing certain types of traffic tocertain types of servers. Typically, most URLs on the same page have thesame serial number to minimize the number of distinguished name (DN)accesses needed per page. This requirement is less important for largerobjects.

Thus, according to the present invention, a virtual server hostname isprepended into the URL for a given embedded object, and this hostnameincludes a value (or serial number) that is generated by applying agiven function to the URL or object. That function may be a hashfunction, an encoding function, or the like.

Turning now back to the flowchart, the routine then continues at step 56to include a given value in the object's URL. Preferably, the givenvalue is generated by applying a given hash function to the embeddedobject. This step creates a unique fingerprint of the object that isuseful for determining whether the object has been modified. Thereafter,the routine returns to step 50 and cycles.

With the above as background, the inventive global hosting framework isnow described in the context of a specific example. In particular, it isassumed that a user of a client machine in Boston requests a ContentProvider Web page normally hosted in Atlanta. For illustrative purposes,it is assumed that the Content Provider is using the global hostingarchitecture within a network, which may be global, international,national, regional, local or private. FIG. 5 shows the variouscomponents of the system and how the request from the client isprocessed. This operation is not to be taken by way of limitation, aswill be explained.

Step 1: The browser sends a request to the Provider's Web site (Item 1).The Content Provider site in Atlanta receives the request in the sameway that it does as if the global hosting framework were not beingimplemented. The difference is in what is returned by the Provider site.Instead of returning the usual page, according to the invention, the Website returns a page with embedded object URLs that are modifiedaccording to the method illustrated in the flowchart of FIG. 4. Aspreviously described, the URLs preferably are changed as follows:

Assume that there are 100,000 virtual ghost servers, even though theremay only be a relatively small number (e.g., 100) physically present onthe network. These virtual ghost servers or virtual ghosts areidentified by the hostname: ghostxxxxx.ghosting.com, where xxxxx isreplaced by a number between 0 and 99,999. After the Content ProviderWeb site is updated with new information, a script executing on theContent Provider site is run that rewrites the embedded URLs.Preferably, the embedded URLs names are hashed into numbers between 0and 99,999, although this range is not a limitation of the presentinvention. An embedded URL is then switched to reference the virtualghost with that number. For example, the following is an embedded URLfrom the Provider's site: <IMGSRC=http://www.provider.com/TECH/images/space.story.gif> If the serialnumber for the object referred to by this URL is the number 1467, thenpreferably the URL is rewritten to read: <IMGSRC=http://ghost467.ghosting.akamai.com/www.provider.com/TECH/images/space.story.gif>.

The use of serial numbers in this manner distributes the embedded URLsroughly evenly over the 100,000 virtual ghost server names. Note thatthe Provider site can still personalize the page by rearranging thevarious objects on the screen according to individual preferences.Moreover, the Provider can also insert advertisements dynamically andcount how many people view each ad.

According to the preferred embodiment, an additional modification to theembedded URLs is made to ensure that the global hosting system does notserve stale information. As previously described, preferably a hash ofthe data contained in the embedded URL is also inserted into theembedded URL itself. That is, each embedded URL may contain afingerprint of the data to which it points. When the underlyinginformation changes, so does the fingerprint, and this prevents usersfrom referencing old data.

The second hash takes as input a stream of bits and outputs what issometimes referred to as a fingerprint of the stream. The importantproperty of the fingerprint is that two different streams almost surelyproduce two different fingerprints. Examples of such hashes are the MD2and MD5 hash functions, however, other more transparent methods such asa simple checksum may be used. For concreteness, assume that the outputof the hash is a 128 bit signature. This signature can be interpreted asa number and then inserted into the embedded URL. For example, if thehash of the data in the picture space.story.gif from the Provider website is the number 28765, then the modified embedded URL would actuallylook as follows:<IMGSRC=http://ghost1467.ghosting.akamai.com/28765/www.provider.com/TECH/images/space.story.gif″>.Whenever a page is changed, preferably the hash for each embedded URL isrecomputed and the URL is rewritten if necessary. If any of the URL'sdata changes, for example, a new and different picture is inserted withthe name space.story.gif, then the hash of the data is different andtherefore the URL itself will be different. This scheme prevents thesystem from serving data that is stale as a result of updates to theoriginal page.

For example, assume that the picture space.story.gif is replaced with amore up-to-date version on the Content Provider server. Because the dataof the pictures changes, the hash of the URL changes as well. Thus, thenew embedded URL looks the same except that a new number is inserted forthe fingerprint. Any user that requests the page after the updatereceives a page that points to the new picture. The old picture is neverreferenced and cannot be mistakenly returned in place of the moreup-to-date information.

In summary, preferably there are two hashing operations that are done tomodify the pages of the Content Provider. First, hashing can be acomponent of the process by which a serial number is selected totransform the domain name into a virtual ghost name. As will be seen,this first transformation serves to redirect clients to the globalhosting system to retrieve the embedded URLs. Next, a hash of the datapointed to by the embedded URLs is computed and inserted into the URL.This second transformation serves to protect against serving stale andout-of-date content from the ghost servers. Preferably, these twotransformations are performed off-line and therefore do not posepotential performance bottlenecks.

Generalizing, the preferred URL schema is as follows. The illustrativedomain www.domainname.com/frontpage.jpg is transformed into:xxxx.yy.zzzz.net/aaaa/www.domainname.com/frontpagejpg, where:

xxxx=serial number fieldyy=lower level DNS fieldzzzz=top level DNS fieldaaaa=other information (e.g., fingerprint) field.

If additional levels of the DNS hierarchy are used, then there may beadditional lower level DNS fields, e.g., xxxx.y.sub.1 y.sub.l.y.sub.2y.sub.2 zzz.net/aaaa/. . . .

Step 2: After receiving the initial page from the Content Provider site,the browser needs to load the embedded URLs to display the page. Thefirst step in doing this is to contact the DNS server on the user'smachine (or at the user's ISP) to resolve the altered hostname, in thiscase: ghost1467.ghosting.akamai.com. As will be seen, the global hostingarchitecture of the present invention manipulates the DNS system so thatthe name is resolved to one of the ghosts that is near the client and islikely to have the page already. To appreciate how this is done, thefollowing describes the progress of the DNS query that was initiated bythe client.

Step 3: As previously described, preferably there are two types of DNSservers in the inventive system: top-level and low-level. The top levelDNS servers 38 for ghosting.com have a special function that isdifferent from regular DNS servers like those of the .com domain. Thetop level DNS servers 38 include appropriate control routines that areused to determine where in the network a user is located, and then todirect the user to a akamai.com (i.e., a low level DNS) server 40 thatis close-by. Like the .com domain, akamai.com preferably has a number oftop-level DNS servers 38 spread throughout the network for faulttolerance. Thus, a given top level DNS server 38 directs the user to aregion in the Internet (having a collection of hosting servers 36 thatmay be used to satisfy the request for a given embedded object) whereasthe low level DNS server 40 (within the identified region) identifies aparticular hosting server within that collection from which the objectis actually served.

More generally, as noted above, the DNS process can contain severallevels of processing, each of which serves to better direct the clientto a ghost server. The ghost server name can also have more fields. Forexample, “a123.g.g.akamaitech.net” may be used instead of“a123.ghost.akamai.com.” If only one DNS level is used, a representativeURL could be “a123.akamai.com.”

Although other techniques may be used, the user's location in thenetwork preferably is deduced by looking at the IP address of the clientmachine making the request. In the present example, the DNS server isrunning on the machine of the user, although this is not a requirement.If the user is using an ISP DNS server, for example, the routines makethe assumption that the user is located near (in the Internet sense)this server. Alternatively, the user's location or IP address could bedirectly encoded into the request sent to the top level DNS. Todetermine the physical location of an IP address in the network,preferably, the top level DNS server builds a network map that is thenused to identify the relevant location.

Thus, for example, when a request comes in to a top level DNS for aresolution for a1234.g.akamaitech.net, the top level DNS looks at thereturn address of the requester and then formulates the response basedon that address according to a network map. In this example, the a1234is a serial number, the g is a field that refers to the lower level DNS,and akamaitech refers to the top level DNS. The network map preferablycontains a list of all Internet Protocol (IP) blocks and, for each IPblock, the map determines where to direct the request. The mappreferably is updated continually based on network conditions andtraffic.

After determining where in the network the request originated, the toplevel DNS server redirects the DNS request to a low level DNS serverclose to the user in the network. The ability to redirect requests is astandard feature in the DNS system. In addition, this redirection can bedone in such a way that if the local low level DNS server is down, thereis a backup server that is contacted.

Preferably, the TTL (time to live) stamp on these top level DNSredirections for the ghosting.com domain is set to be long. This allowsDNS caching at the user's DNS servers and/or the ISP's DNS servers toprevent the top level DNS servers from being overloaded. If the TTL forghosting.akamai.com in the DNS server at the user's machine or ISP hasexpired, then a top level server is contacted, and a new redirection toa local low level ghosting.akamai.com DNS server is returned with a newTTL stamp. It should be noted the system does not cause a substantiallylarger number of top level DNS lookups than what is done in the currentcentralized hosting solutions. This is because the TTL of the top levelredirections are set to be high and, thus, the vast majority of usersare directed by their local DNS straight to a nearby low levelghosting.akamai.com DNS server.

Moreover, fault tolerance for the top level DNS servers is providedautomatically by DNS similarly to what is done for the popular .comdomain. Fault tolerance for the low level DNS servers preferably isprovided by returning a list of possible low level DNS servers insteadof just a single server. If one of the low level DNS servers is down,the user will still be able to contact one on the list that is up andrunning.

Fault tolerance can also be handled via an “overflow control” mechanismwherein the client is redirected to a low-level DNS in a region that isknown to have sufficient capacity to serve the object. This alternateapproach is very useful in scenarios where there is a large amount ofdemand from a specific region or when there is reduced capacity in aregion. In general, the clients are directed to regions in a way thatminimizes the overall latency experienced by clients subject to theconstraint that no region becomes overloaded. Minimizing overall latencysubject to the regional capacity constraints preferably is achievedusing a min-cost multi-commodity flow algorithm.

Step 4: At this point, the user has the address of a close-byghosting.com DNS server 38. The user's local DNS server contacts theclose-by low level DNS server 40 and requests a translation for the nameghost1467.ghosting.akamai.com. The local DNS server is responsible forreturning the IP address of one of the ghost servers 36 on the networkthat is close to the user, not overloaded, and most likely to alreadyhave the required data.

The basic mechanism for mapping the virtual ghost names to real ghostsis hashing. One preferred technique is so-called consistent hashing, asdescribed in U.S. Ser. No. 09/042,228, filed Mar. 13, 1998, and in U.S.Ser. No. 09/088,825, filed Jun. 2, 1998, each titled Method AndApparatus For Distributing Requests Among A Plurality Of Resources, andowned by the Massachusetts Institute of Technology, which applicationsare incorporated herein by reference. Consistent hash functions make thesystem robust under machine failures and crashes. It also allows thesystem to grow gracefully, without changing where most items are locatedand without perfect information about the system.

According to the invention, the virtual ghost names may be hashed intoreal ghost addresses using a table lookup, where the table iscontinually updated based on network conditions and traffic in such away to insure load balancing and fault tolerance. Preferably, a table ofresolutions is created for each serial number. For example, serialnumber 1 resolves to ghost 2 and 5, serial number 2 resolves to ghost 3,serial number 3 resolves to ghosts 2, 3, 4, and so forth. The goal is todefine the resolutions so that no ghost exceeds its capacity and thatthe total number of all ghosts in all resolutions is minimized. This isdone to assure that the system can take maximal advantage of theavailable memory at each region. This is a major advantage over existingload balancing schemes that tend to cache everything everywhere or thatonly cache certain objects in certain locations no matter what the loadsare. In general, it is desirable to make assignments so that resolutionstend to stay consistent over time provided that the loads do not changetoo much in a short period of time. This mechanism preferably also takesinto account how close the ghost is to the user, and how heavily loadedthe ghost is at the moment.

Note that the same virtual ghost preferably is translated to differentreal ghost addresses according to where the user is located in thenetwork. For example, assume that ghost server 18.98.0.17 is located inthe United States and that ghost server 132.68.1.28 is located inIsrael. A DNS request for ghost1487.ghosting.akamai.com originating inBoston will resolve to 18.98.0.17, while a request originating inTel-Aviv will resolve to 132.68.1.28.

The low-level DNS servers monitor the various ghost servers to take intoaccount their loads while translating virtual ghost names into realaddresses. This is handled by a software routine that runs on the ghostsand on the low level DNS servers. In one embodiment, the loadinformation is circulated among the servers in a region so that they cancompute resolutions for each serial number. One algorithm for computingresolutions works as follows. The server first computes the projectedload (based on number of user requests) for each serial number. Theserial numbers are then processed in increasing order of load. For eachserial number, a random priority list of desired servers is assignedusing a consistent hashing method. Each serial number is then resolvedto the smallest initial segment of servers from the priority list sothat no server becomes overloaded. For example, if the priority list fora serial number is 2, 5, 3, 1, 6, then an attempt is made first to tryto map the load for the serial number to ghost 2. If this overloadsghost 2, then the load is assigned to both ghosts 2 and 5. If thisproduced too much load on either of those servers, then the load isassigned to ghosts 2, 3, and 5, and so forth. The projected load on aserver can be computed by looking at all resolutions that contain thatserver and by adding the amount of load that is likely to be sent tothat server from that serial number. This method of producingresolutions is most effective when used in an iterative fashion, whereinthe assignments start in a default state, where every serial number ismapped to every ghost. By refining the resolution table according to theprevious procedure, the load is balanced using the minimum amount ofreplication (thereby maximally conserving the available memory in aregion).

The TTL for these low level DNS translations is set to be short to allowa quick response when heavy load is detected on one of the ghosts. TheTTL is a parameter that can be manipulated by the system to insure abalance between timely response to high load on ghosts and the loadinduced on the low level DNS servers. Note, however, that even if theTTL for the low level DNS translation is set to 1-2 minutes, only a fewof the users actually have to do a low level DNS lookup. Most users willsee a DNS translation that is cached on their machine or at their ISP.Thus, most users go directly from their local DNS server to the close-byghost that has the data they want. Those users that actually do a lowlevel DNS lookup have a very small added latency, however this latencyis small compared to the advantage of retrieving most of the data fromclose by.

As noted above, fault tolerance for the low level DNS servers isprovided by having the top level DNS return a list of possible low levelDNS servers instead of a single server address. The user's DNS systemcaches this list (part of the standard DNS system), and contacts one ofthe other servers on the list if the first one is down for some reason.The low level DNS servers make use of a standard feature of DNS toprovide an extra level of fault tolerance for the ghost servers. When aname is translated, instead of returning a single name, a list of namesis returned. If for some reason the primary fault tolerance method forthe ghosts (known as the Buddy system, which is described below) fails,the client browser will contact one of the other ghosts on the list.

Step 5: The browser then makes a request for an object nameda123.ghosting.akamai.com/.../www.provider.com/TECH/images/space.story.giffrom the close-by ghost. Note that the name of the original server(www.provider.com) preferably is included as part of the URL. Thesoftware running on the ghost parses the page name into the originalhost name and the real page name. If a copy of the file is alreadystored on the ghost, then the data is returned immediately. If, however,no copy of the data on the ghost exists, a copy is retrieved from theoriginal server or another ghost server. Note that the ghost knows whothe original server was because the name was encoded into the URL thatwas passed to the ghost from the browser. Once a copy has been retrievedit is returned to the user, and preferably it is also stored on theghost for answering future requests.

As an additional safeguard, it may be preferable to check that the useris indeed close to the server. This can be done by examining the IPaddress of the client before responding to the request for the file.This is useful in the rare case when the client's DNS server is far awayfrom the client. In such a case, the ghost server can redirect the userto a closer server (or to another virtual address that is likely to beresolved to a server that is closer to the client). If the redirect isto a virtual server, then it must be tagged to prevent furtherredirections from taking place. In the preferred embodiment, redirectionwould only be done for large objects; thus, a check may be made beforeapplying a redirection to be sure that the object being requestedexceeds a certain overall size.

Performance for long downloads can also be improved by dynamicallychanging the server to which a client is connected based on changingnetwork conditions. This is especially helpful for audio and videodownloads (where the connections can be long and where quality isespecially important). In such cases, the user can be directed to analternate server in mid-stream. The control structure for redirectingthe client can be similar to that described above, but it can alsoinclude software that is placed in the client's browser or media player.The software monitors the performance of the client's connection andperhaps the status of the network as well. If it is deemed that theclient's connection can be improved by changing the server, then thesystem directs the client to a new server for the rest of theconnection.

Fault tolerance for the ghosts is provided by a buddy system, where eachghost has a designated buddy ghost. If a ghost goes down, its buddytakes over its work (and IP address) so that service is not interrupted.Another feature of the system is that the buddy ghost does not have tosit idle waiting for a failure. Instead, all of the machines are alwaysactive, and when a failure happens, the load is taken over by the buddyand then balanced by the low level DNS system to the other activeghosts. An additional feature of the buddy system is that faulttolerance is provided without having to wait for long Timeout periods.

As yet another safety feature of the global hosting system, a gatingmechanism can be used to keep the overall traffic for certain objectswithin specified limits. One embodiment of the gating mechanism works asfollows. When the number of requests for an object exceeds a certainspecified threshold, then the server can elect to not serve the object.This can be very useful if the object is very large. Instead, the clientcan be served a much smaller object that asks the client to returnlater. Or, the client can be redirected. Another method of implementinga gate is to provide the client with a “ticket” that allows the clientto receive the object at a pre-specified future time. In this method,the ghost server needs to check the time on the ticket before servingthe object.

The inventive global hosting scheme is a way for global ISPs orconglomerates of regional ISPs to leverage their network infrastructureto generate hosting revenue, and to save on network bandwidth. An ISPoffering the inventive global hosting scheme can give content providersthe ability to distribute content to their users from the closest pointon the ISPs network, thus ensuring fast and reliable access. Guaranteedweb site performance is critical for any web-based business, and globalhosting allows for the creation of a service that satisfies this need.

Global hosting according to the present invention also allows an ISP tocontrol how and where content traverses its network. Global hostingservers can be set up at the edges of the ISP's network (at the manynetwork exchange and access points, for example). This enables the ISPto serve content for sites that it hosts directly into the networkexchange points and access points. Expensive backbone links no longerhave to carry redundant traffic from the content provider's site to thenetwork exchange and access points. Instead, the content is serveddirectly out of the ISP's network, freeing valuable network resourcesfor other traffic.

Although global hosting reduces network traffic, it is also a method bywhich global ISPs may capture a piece of the rapidly expanding hostingmarket, which is currently estimated at over a billion dollars a year.

The global hosting solution also provides numerous advantages to ContentProviders, and, in particular, an efficient and cost-effective solutionto improve the performance of their Web sites both domestically andinternationally. The inventive hosting software ensures ContentProviders with fast and reliable Internet access by providing a means todistribute content to their subscribers from the closest point on anISP's network. In addition to other benefits described in more detailbelow, the global hosting solution also provides the important benefitof reducing network traffic.

Once inexpensive global hosting servers are installed at the peripheryof an ISP's network (i.e., at the many network exchange and accesspoints), content is served directly into network exchange and accesspoints. As a result of this efficient distribution of content directlyfrom an ISP's network, the present invention substantially improves Website performance. In contrast to current content distribution systems,the inventive global hosting solution does not require expensivebackbone links to carry redundant traffic from the Content Provider'sWeb site to the network exchange and access points.

A summary of the specific advantages afforded by the inventive globalhosting scheme are set forth below:

1. Decreased Operational Expenses for Content Providers:

Most competing solutions require Content Providers to purchase serversat each Web site that hosts their content. As a result, ContentProviders often must negotiate separate contracts with different ISPsaround the world. In addition, Content Providers are generallyresponsible for replicating the content and maintaining servers in theseremote locations.

With the present invention, ISPs are primarily responsible for themajority of the aspects of the global hosting. Content Providerspreferably maintain only their single source server. Content on thisserver is automatically replicated by software to the locations where itis being accessed. No intervention or planning is needed by the Provider(or, for that matter, the ISP). Content Providers are offered instantaccess to all of the servers on the global network; there is no need tochoose where content should be replicated or to purchase additionalservers in remote locations.

2. Intelligent and Efficient Data Replication:

Most competing solutions require Content Providers to replicate theircontent on servers at a commercial hosting site or to minor theircontent on geographically distant servers. Neither approach isparticularly efficient. In the former situation, content is stilllocated at a single location on the Internet (and thus it is far awayfrom most users). In the latter case, the entire content of a Web siteis copied to remote servers, even though only a small portion of thecontent may actually need to be located remotely. Even with inexpensivememory, the excessive cost associated with such mirroring makes ituneconomical to minor to more than a few sites, which means that mostusers will still be far away from a mirror site. Mirroring also has theadded disadvantage that Content Providers must insure that all sitesremain consistent and current, which is a nontrivial task for even a fewsites.

With the present invention, content is automatically replicated to theglobal server network in an intelligent and efficient fashion. Contentis replicated in only those locations where it is needed. Moreover, whenthe content changes, new copies preferably are replicated automaticallythroughout the network.

3. Automatic Content Management:

Many existing solutions require active management of contentdistribution, content replication and load balancing between differentservers. In particular, decisions about where content will be hostedmust be made manually, and the process of replicating data is handled ina centralized push fashion. On the contrary, the invention featurespassive management. Replication is done in a demand-based pull fashionso that content preferably is only sent to where it is truly needed.Moreover, the process preferably is fully automated; the ISP does nothave to worry about how and where content is replicated and/or thecontent provider.

4. Unlimited, Cost Effective Scalability:

Competing solutions are not scalable to more than a small number ofsites. For example, solutions based on mirroring are typically used inconnection with at most three or four sites. The barriers to scalinginclude the expense of replicating the entire site, the cost ofreplicating computing resources at all nodes, and the complexity ofsupporting the widely varying software packages that Content Providersuse on their servers.

The unique system architecture of the present invention is scaleable tohundreds, thousands or even millions of nodes. Servers in the hostingnetwork can malfunction or crash and the system's overall function isnot affected. The global hosting framework makes efficient use ofresources; servers and client software do not need to be replicated atevery node because only the hosting server runs at each node. Inaddition, the global hosting server is designed to run on standardsimple hardware that is not required to be highly fault tolerant.

5. Protection against Flash Crowds:

Competing solutions do not provide the Content Provider with protectionfrom unexpected flash crowds. Although mirroring and relatedload-balancing solutions do allow a Content Provider to distribute loadacross a collection of servers, the aggregate capacity of the serversmust be sufficient to handle peak demands. This means that the Providermust purchase and maintain a level of resources commensurate with theanticipated peak load instead of the true average load. Given the highlyvariable and unpredictable nature of the Internet, such solutions areexpensive and highly wasteful of resources.

The inventive hosting architecture allows ISPs to utilize a singlenetwork of hosting servers to offer Content Providers flash crowdinsurance. That is, insurance that the network will automatically adaptto and support unexpected higher load on the Provider's site. Becausethe ISP is aggregating many Providers together on the same globalnetwork, resources are more efficiently used.

6. Substantial Bandwidth Savings:

Competing solutions do not afford substantial bandwidth savings to ISPsor Content Providers. Through the use of minoring, it is possible tosave bandwidth over certain links (i.e., between New York and LosAngeles). Without global hosting, however, most requests for contentwill still need to transit the Internet, thus incurring bandwidth costs.The inventive hosting framework saves substantial backbone bandwidth forISPs that have their own backbones. Because content is distributedthroughout the network and can be placed next to network exchangepoints, both ISPs and Content Providers experience substantial savingsbecause backbone charges are not incurred for most content requests.

7. Instant Access to the Global Network:

Competing solutions require the Content Provider to choose manually asmall collection of sites at which content will be hosted and/orreplicated. Even if the ISP has numerous hosting sites in widely variedlocations, only those sites specifically chosen (and paid for) will beused to host content for that Content Provider.

On the contrary, the global hosting solution of the present inventionallows ISPs to offer their clients instant access to the global networkof servers. To provide instant access to the global network, content ispreferably constantly and dynamically moved around the network. Forexample, if a Content Provider adds content that will be of interest tocustomers located in Asia, the Content Provider will be assured that itscontent will be automatically moved to servers that are also located inAsia. In addition, the global hosting framework allows the content to bemoved very close to end users (even as close as the user's building inthe case of the Enterprise market).

8. Designed for Global ISPs and Conglomerates:

Most competing solutions are designed to be purchased and managed byContent Providers, many of whom are already consistently challenged andconsumed by the administrative and operational tasks of managing asingle server. The inventive hosting scheme may be deployed by a globalISP, and it provides a new service that can be offered to ContentProviders. A feature of the service is that it minimizes the operationaland managerial requirements of a Content Provider, thus allowing theContent Provider to focus on its core business of creating uniquecontent.

9. Effective Control of Proprietary Databases and ConfidentialInformation:

Many competing solutions require Content Providers to replicate theirproprietary databases to multiple geographically distant sites. As aresult, the Content Provider effectively loses control over itsproprietary and usually confidential databases. To remedy theseproblems, the global hosting solution of the present invention ensuresthat Content Providers retain complete control over their databases. Asdescribed above, initial requests for content are directed to theContent Provider's central Web site, which then implements effective andcontrolled database access. Preferably, high-bandwidth, static parts forpage requests are retrieved from the global hosting network.

10. Compatibility with Content Provider Software:

Many competing solutions require Content Provider s to utilize aspecific set of servers and databases. These particular, non-uniformrequirements constrain the Content Provider's ability to mosteffectively use new technologies, and may require expensive changes to aContent Provider's existing infrastructure. By eliminating theseproblems, the inventive global hosting architecture effectivelyinterfaces between the Content Provider and the ISP, and it does notmake any assumptions about the systems or servers used by the ContentProvider. Furthermore, the Content Provider's systems can be upgraded,changed or completely replaced without modifying or interrupting theinventive architecture.

11. No Interference with Dynamic Content, Personalized Advertising orE-Commerce, and No stale content:

Many competing solutions (such as naive caching of all content) caninterfere with dynamic content, personalized advertising and E-commerceand can serve the user with stale content. While other softwarecompanies have attempted to partially eliminate these issues (such askeeping counts on hits for all cached copies), each of these solutionscauses a partial or complete loss of functionality (such as the abilityto personalize advertising). On the contrary, the global hostingsolution does not interfere with generation of dynamic content,personalized advertising or E-commerce, because each of these taskspreferably is handled by the central server of the Content Provider.

12. Designed for the Global Network:

The global hosting architecture is highly scaleable and thus may bedeployed on a world-wide network basis.

The above-described functionality of each of the components of theglobal hosting architecture preferably is implemented in softwareexecutable in a processor, namely, as a set of instructions or programcode in a code module resident in the random access memory of thecomputer. Until required by the computer, the set of instructions may bestored in another computer memory, for example, in a hard disk drive, orin a removable memory such as an optical disk (for eventual use in a CDROM) or floppy disk (for eventual use in a floppy disk drive), ordownloaded via the Internet or other computer network.

In addition, although the various methods described are convenientlyimplemented in a general purpose computer selectively activated orreconfigured by software, one of ordinary skill in the art would alsorecognize that such methods may be carried out in hardware, in firmware,or in more specialized apparatus constructed to perform the requiredmethod steps.

Further, as used herein, a Web “client” should be broadly construed tomean any computer or component thereof directly or indirectly connectedor connectable in any known or later-developed manner to a computernetwork, such as the Internet. The term Web “server” should also bebroadly construed to mean a computer, computer platform, an adjunct to acomputer or platform, or any component thereof. Of course, a “client”should be broadly construed to mean one who requests or gets the file,and “server” is the entity which downloads the file.

1. A computer-implemented method of delivering text, graphics, images,downloads, audio or video on behalf of multiple content providers,comprising: operating content delivery network (CDN) content servers inmultiple locations; operating multiple CDN name servers; having a firstCDN name server respond to a first domain name service (DNS) query byissuing a first response that includes a first set of one or more IPaddresses, the first DNS query originating from a first local DNS nameserver and including at least a portion of an IP address of a machineassociated with the first local DNS name server; receiving a first enduser request for content issued by the machine and directed to one ofthe IP addresses of the first set, the first end user request requestingdelivery of content to the machine from a first CDN content server, thefirst CDN content server located in a first location of the multiplelocations; and following the sending of the first response, and upondetermining based upon the IP address associated with the machine thatthe first local DNS name server is located remotely from the machine,issuing a second response that attempts to direct the machine closer toa CDN content server located in a second location of the multiplelocations, the second location being closer to the machine than thefirst location.
 2. The method as described in claim 1 wherein the secondresponse is a redirection.
 3. The method as described in claim 1 whereinthe second response comprises a virtual address.
 4. The method asdescribed in claim 1 wherein the second response comprises a set of oneor more IP addresses that includes an IP address.
 5. The method asdescribed in claim 4 wherein the IP address is associated with CDNcontent server in the second location.
 6. The method as described inclaim 1 wherein the IP address associated with the machine is encodedinto the first DNS query.
 7. The method as described in claim 2 furtherincluding restricting redirection to a single occurrence.